A Dose-Effect Relationship and Estimated Parameters for the Lyman-Kutcher-Burman (LKB) Model of Normal Tissue Complication Probability (NTCP) for Radiation-Induced Hypothyroidism

Results:Median follow up was 5.1 months. 8 patients had an oropharyngeal primary and 2 had an unknown primary. The T stagewas T1 in 1, T2 in 4, T3 in 3, and Tx in 2. Lymph node staging was N1 in 0, N2 in 9, and N3 in 1. 8 patients were HPV+ and 2 were HPV negative. The median number of ontreatment MRIs per each patient was 5 (range: 3 6). Median volumes for parotids and submandibular glands (SMG) were 37.1 cc and 10.8 cc respectively. Median % change in volume for parotids and submandibular glands were -8% (range: -40% +13%) and -18% (range: -69% +14%). Maximum mucositis during RT was grade 3 in 50% of patients, grade 2 in 30%, and grade 1 in 20%. Maximum xerostomia was grade 2 in 40% of patients and grade 1 in 60%. Maximum dysphagia was grade 3 in 10% of patients, grade 2 in 40% of patients, and grade 1 in 50% of patients. On univariate analysis, change in parotid volume correlated with dysphagia (p Z 0.008) and functional mucositis (p Z 0.0005), while change in SMG volume correlated with xerostomia (pZ 0.048). With multivariate analysis, the change in SMG volume correlated with xerostomia (pZ 0.047), and the change in parotid volume correlated with dysphagia (p Z 0.019). Conclusions: MRI demonstrates significant volumetric changes in the salivary glands with large inter-individual patient differences. Although volume changes in the salivary glands correlate with acute toxicity, more follow up is needed to determine if these changes also correlate with long term toxicity. Further study is warranted in a larger patient cohort to determine how volumetric changes in normal tissues affect quality of life outcomes. Author Disclosure: J. Han: None. N. Tyagi: None. S. Kamran: None. S. McBride: None. N. Riaz: None. N. Lee: None.